Reijo Sillanpää

Modulation of the CC distance in disubstituted l,2-R2-o-carboranes. Crystal structure of closo l,2-(SPh)2-l,2-C2B10H10

Abstract 1,2-Cc-substituted o-carboranes, where Cc represents the cluster carbon atoms, display a range of experimental/computed Cc⋯Cc distances from 1.629/1.624 A for the unsubstituted parent compound 1,2-C2B10H12 (1) to 1.798/1.818 A for l,2-(SPh)2-l,2-C2B10H10 (5) 1 or 1.858(5)/1.826(5) for l,2-μ-SCH2(CH2OCH2)2CH2S-1,2-C2B10H10 (7). Different Cc⋯Cc distances can be achieved by modifying the substituents on the carbon of the cluster compound. The crystal structure of a new disubstituted o-carborane 1,2-(SPh)2-l,2-C2B10H10 (5) was elucidated by single crystal X-ray diffraction. Purely alkyl substituents alter the Cc⋯Cc distance of the parent compound very little, which implies that steric effects, although relevant, are not the major cause of the lengthening. In contrast, substituents with lone pairs alter the Cc⋯Cc distance substantially. Our calculations suggest that the cause of the elongation is the transfer of electron density from the available lone pairs on the substituents to the Ψ* low-lying virtual orbitals mainly distributed around Cc, producing a decrease in the Cc⋯Cc bond order and, thereby, an increase in the Cc⋯Cc distance. A Bader analysis shows that the electron density at the bond-critical point, which is found at the mid-point of the Cc⋯Cc distance, decreases considerably with the presence of lone pairs of the sulfur atoms bound to the Cc atoms of the carborane cage.

cis-Dioxomolybdenum(VI) complexes with tridentate and tetradentate Schiff base ligands. Preparation, structures and inhibition of aerial oxidation of aldehydes

Abstract The synthesis and characterisation of four monomeric cis -dioxomolybdenum(VI) complexes involving Schiff base ligands is described. Ligands were obtained by condensation of salicylaldehyde with substituted aminoethanols. [MoO 2 (acac) 2 ] reacted with the prepared ligands forming six-coordinated cis -dioxoMo(VI) complexes. X-ray diffraction studies confirmed that ligands act in a tridentate manner and the sixth coordination site around Mo(VI) is occupied by methanol used as solvent. The complexes act as inhibitors in the oxidation of aldehydes by oxygen.

The formation of nido [7,8-(PR2)2-7,8-C2B9H10]− from closo 1,2−(PR2)2−1,2−C2B10H10 (R = Ph, Et, iPr or OEt): a process enhanced by complexation

Abstract To gain insight into the mutual influence of an electron-rich element directly connected to the carborane cage, the coordination behavior of phosphorus atoms directly bonded to the cage has been studied. The reactivity of bisphosphines [7,8−(PR2)2−7,8−C2B9H10]− ( R = Ph, Et, i Pr or OEt ) has been investigated. These new chelating ligands exhibit some similarities to the much used 1,2-diphenylphosphinoethane (diphos), such as the spacing between the two phosphorus atoms, and their five-membered ring chelating ability, but there are notable differences, and dissimilar ligating properties are expected. The differences are mainly due to the incorporated carborane cluster and can be summarized as follows: (1) the ligand is anionic, (2) the phosphorus atoms lie in an eclipsed conformation and (3) B(3)−H coordination to the metal is possible. To study the partial degradation of the closo clusters to the nido clusters enhanced by complexation, several metal complexes were treated with the closo ligands in ethanol. The crystal structures of [AuCl2 {7,8−(P(iPr2)2−7,8−C2B9H10}] and [RuCl2{7,8−(P(iPr2)2−7,8−C2B9H10}2] have been determined.

Procedure for the degradation of 1,2-(PR2)2-1,2-dicarba-closo-dodecaborane(12) and 1-(PR2)-2-R′-1,2-dicarba-closo-dodecaborane(12)

Abstract Monophosphines and bisphosphines bearing anionic groups derived from the 7,8-dicarba- nido -undecaborate unit, such as [7-PR 2 -8-Me-7,8-C 2 B 9 H 10 ] − and [7,8-(PR 2 ) 2 -7,8-C 2 B 9 H 10 ] − (R = phenyl, ethyl, isopropyl or ethoxy), were synthesized from closo -carborane precursors 1-PR 2 -2-Me-1,2-C 2 B 10 H 10 and 1,2-(PR 2 ) 2 -1,2-C 2 B 10 H 10 , respectively. In general, the C c P bond in the closo species is very susceptible degradation reactions, producing C c P cleavage and yielding the [7,8-C 2 B 9 H 10 ] 2 − anion. Good degradation conditions which retain the C c P found are toluene with a carborane-to-pipeeridine ratio of 1:50 and ethanol with carborane-to-piperidine ratio of 1:10. The aryl phosphines keep the C c P bond best and produce the highest yields. Phosphites also retain the C c P bond, but the phosphorus becomes positive and produces a zwitterionic species. Alkylphosphines are intermediate, depending on the bulk and nature of the R group in the −PR 2 unit. The crystal structure of [NMe 4 ][7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ]·CH 3 CH 2 OH is described.

Reactions of Pd(II) with closo-1,2-dicarbadodecaborane-1,2-diphosphines

Abstract The reactivity of carboranyldiphosphines towards palladium (II) complexes and the modifications that take place on the cluster are studied in this work. The reaction of aryl, alkyl or alkoxy substituted closo-carboranyldiphosphines with palladium (II) complexes [PdCl2L2] (L=PPh3, PMePh2, PhCN) in ethanol, yields products in which partial degradation of the carborane cage has taken place and total or partial substitution of the chlorine atoms of the initial palladium (II) complex has been observed. The final stoichiometry depends on the steric characteristics of the ligand, their basicity and the starting Pd(II) complex. The crystal structure of [Pd2(μ-Cl)2{7,8-(PiPr2)2-7,8-C2Bq9H10}2] the third structurally characterized example of a bis chloride bridged palladium complex with phosphines has been determined.

Contribution of the o-carboranyl fragment to the chemical stability and the 31P-NMR chemical shift in closo-carboranylphosphines. Crystal structure of bis(1-yl-2-methyl-1,2-dicarba-closo-dodecaborane)phenylphosphine

Abstract Closo-carboranylphosphines behave differently from closo-monothiocarboranes or other organophosphorus compounds. They tend to lose one boron by reacting with a nucleophile such as OH− with hydrolysis of the CP bond. On the other hand, they are less basic than similar organophosphorus compounds, and less reactive both towards oxygen and some metal ions. Many or all of these characteristics can be attributed to the carborane cluster. Its influence on the phosphorus has been revealed by studying the 31P chemical shifts of a series of P(L)R2 and P(L)2R phosphines, where L are different carboranyl fragments. If the series P(L)Ph2 is considered, where a phosphorus atom is surrounded by two phenyl groups and one o-carboranyl moiety carbon bonded to the phosphorus, it is observed that the capacity to shift the 31P-NMR resonances of P(L)Ph2 to lower field follows the trend: 1-yl-1,2-dicarba-closo-dodecaborane>1-yl-2-phenyl-1,2-dicarba-closo-dodecaborane>1-yl-2-methyl-1,2-dicarba-closo-dodecaborane. These trends are valid for any P(L)R2 series tested so far. It is also found that the absolute value of the 1J(PC(1)) coupling constants, where C(1) is the cluster carbon bonded to P atom, also displays the same trend. The molecular structure of bis(1-yl-2-methyl-1,2-dicarba-closo-dodecaborane)phenylphosphine is presented in this paper.

Synthesis of all four enantiomers of 1-aminoindane-2-carboxylic acid, a new cispentacin benzologue

Abstract Racemic cis- and trans -1-aminoindane-2-carboxylic acids ( 3 and 5 ) were prepared from indene by chlorosulphonyl isocyanate addition followed by ring opening and isomerisation. The intermediate racemic hydroxymethylated β-lactam 6 was resolved through the lipase-catalysed asymmetric acylation of the primary hydroxy group at the ( R )-stereogenic centre. High enantioselectivities ( E >200) were observed when the enzymatic reactions were performed with lipase AK or lipase PS as catalyst and vinyl acetate or vinyl butyrate as acyl donor. The hydrolysis and isomerisation resulted in all four enantiomers ( 9 , 11 , 13 and 14 ) of 1-aminoindane-2-carboxylic acid, a new benzologue of cispentacin.

Substituent effects on the ring-chain tautomerism of 1,3-oxazines

Abstract The aryl substituents at positions 4 and 6 do not exert observable electronic effects on the ring-chain tautomeric ratios of 2,4- or 2,6-diarylsubstituted-tetrahydro-1,3-oxazines. On the other hand, the electronic effect of the 2-aryl substituent is marked: in all eight series studied, the equilibria can be described by the equation log K = ϱ σ+ +log K0, where ϱ+ is the Hammett-Brown constant of the 2-aryl substituents, and ϱ is a constant characteristic of the ring system (=0.75±0.05).

Synthesis, characterization, crystal structures and magnetic exchange in dinuclear copper complexes with 3-amino-1-propanol as terminal and bridging ligand

Abstract The synthesis, X-ray structures and spectroscopic and magnetic properties are described for two groups of dinuclear Cu(II) compounds with the ligand 3-amino-1-propanol (Hap). The formulae of the compounds are for group A: [Cu(ap)(anion)]2, in which ap is the dehydronated Hap and the anions are formate, nitrate, chloride and bromide and for group B: [Cu(ap)(Hap)]2(anion)2, with anion = iodide, bromide, chloride, nitrate and tetrafluoroborate. The structure of group A compounds consists of dinuclear units with the co-planar centrosymmetric chromophore ANCuOO′CuNA, in which the A ligands (anions) bridge to neighbouring units as axial ligands, thereby forming infinite chains. Dimer Cu…Cu distances are about 295 pm. The X-ray structure of [Cu(ap)(NO3)]2 (I) is described in detail. Dark blue crystals of I were studied with single crystal X-ray measurements and refined to a final R value of 0.025 for 1440 reflections. The compound crystallizes in the monoclinic space group P21/c with two dimeric molecules in a cell of dimensions a = 886.56(5), b = 815.92(6), c = 928.71(3) pm and β = 104.671(4)°. The structure consists of centrosymmetric di-alkoxy bridged dimers in which the Cu…Cu distance is 293.91(3) pm. The dimers are polymerized along the c axis into chains via NHO hydrogen bonds. These chains are joined together along the b axis by CuONOCu bridges and weak NHO hydrogen bonds. This results in layers, which are held together by van der Waals forces. The copper(II) ions have a distorted square pyramidal geometry, which is close to a tetragonally distorted octahedral coordination sphere. The structure of group B compounds consists of dinuclear units with the centrosymmetric chromophore [LNCuOO′CuNL] in which L is an N-coordinating Hap ligand. The alcoholic function of Hap coordinates as an axial ligand to neighbouring dimeric units, forming again an infinite chain structure. Dimeric Cu…Cu distances are 303 pm. The anions in structure B are not coordinated to copper, but are hydrogen bonded to the ligand NH and OH groups. Ligand-field spectra agree with square-pyramidal (4 + 1) or distorted octahedral (4 + 1 + 1) coordination geometries for Cu(II) in all cases. Small differences in ligand-field spectra are ascribed to differences in anions and axial CuO distances. The compounds are all very strongly magnetically coupled, as seen from the fact that they are diamagnetic at low temperatures. Both groups of compounds have been studied with magnetic susceptibility measurements in the 2–400 K region and the data could be fitted with the Bleaney-Bowers equation for dimers. Compounds of type A have much smaller values of -2J than those of type B. This nicely agrees with the larger value of the CuOCu angles in the case of group B (99.5–7° in A, against 103.5°). EPR spectra of the compounds show mainly small paramagnetic impurities (below 1%) in agreement with the dimeric structure.

Synthesis and stereochemistry of 1,3,2-oxazaphosphorino [4,3-A]isoquinolines

Abstract 1,3,2-Oxazaphosphorino[4,3- a ]isoquinolines 8a,b, 9a,b and 10a were synthesized by the reactions of homocalycotomine 7 with appropriate dichlorophosphorus derivatives, such as phenylphosphonic dichloride, bis(2-chloroethyl)phosphonic dichloride or phosphoryl chloride. In spite of the blocking effect of the connecting isoquinoline ring system, the oxazaphosphorinane moiety exists as a chair–twist equilibrium, where the conformer ratios are strongly dependent on the P-4 configuration and the stereoelectronic properties of the substituents.